
We conceive a system model of UAV-assisted IoT wireless power transfer with the support of a RIS. The IoT devices harvest energy in the downlink and transmit information in the uplink to the UAVs.

To characterise the agility of UAV in supporting the energy harvesting (EH) and information transmission of IoT devices, we consider two scenarios of UAV. Firstly, the UAV is hovering at the centre of the cluster and provides energy to the IoT devices. The RIS helps alleviate the uplink interference when the IoT devices transmit their information to the UAV. Secondly, the UAV is deployed in an initial location and required to find a better location for communication. In each location of the UAV's flying trajectory, the EH time scheduling and the RIS's phase shift matrix are optimized for maximizing the network throughput performance.

For the defined problem, we formulate a Markov decision process (MDP) [1]} with the definition of the state space, action space and the reward function. Then, we propose a method based on deep deterministic policy gradient (DDPG) and proximal policy optimization algorithm (PPO) for solving the maximization game.

Our results suggest that with the support of the RIS, a better connection is established and the overall performance is significantly improved.

